Police surround the booby-trapped apartment of suspect James Holmes, which was booby-trapped with explosives. Photograph: Kevork Djansezian/Getty Images

Joanne Southard has probably never had a greater vindication of her gut instincts than her decision last April to refuse to rent an apartment to James Holmes.

Now, in a building just a block away from the one the 55-year-old manages, Holmes' own apartment is a potentially lethal booby-trap filled with jars of unknown liquids, ammunition, tripwires and possible bombs.

Of course, at the time she rejected him, Southard had no inkling the neat and tidy young man in front of her had the potential to walk into a cinema and shoot 12 people dead.

She was more concerned with his failure to return phone calls or even answer the phone when she rang him.

"Thank God I had a sixth sense, otherwise he might have tried to build that thing in one of my apartments," she said.

Holmes' references for an apartment building were actually good.

"They said he was quiet. He was happy," she said. His arrest record was also a blank, save for a single speeding ticket.

All in all, that made him a potential model tenant in this rundown section of Aurora, full of working class apartment buildings and rundown houses.

But Southard turned him down. "He seemed nice. Clean cut. But I guess there was something just a little off. He seemed unreliable. So I said no," she said.

Instead Holmes ended up renting a different apartment in another building just a few hundred yards away.

That building is now evacuated and surrounded by police tape. Inside dozens of police and firemen are striving to defuse the traps and devices that Holmes left behind.